New operator to match flags stored in hstore

Could not find a different solution than to create a special operator for this use case. Feedback is very welcomed.
Not sure how much time it will take to make such change, I will probably need to change the way how the rules are parsed. There is not a single check that works this way
```ruby 
:attribute => { :some_other_attribute operator value } 
```
IMO, there is a reason why almost every operator in declarative_auth has a reverse version. If we **really** need the reverse version then I think we should go the same route.
```ruby
if_attribute :permissions_flags => flag_disabled { :testing }
```
Plus, if we choose this path - we can add the additional operator later when it's really needed. For current RBO settings change it's not necessary.